1. Field of Invention
This invention relates to submerged arc welding; more specifically the application of a weld overlay to the interior surface of angular, hollow vessels.
2. Description of Prior Art
Since the introduction of electroslag welding by the USSR at the Brussel's World Fair in 1958, many advancements in the art have occured, particularly in respect to electroslag surfacing, where much has been gained both technically and economically.
At the most basic level, welding is a process in which two materials -usually metals-are permanently joined together by coalescense resulting from a combination of temperature, pressure and metallurgical conditions. The particular combination of temperature and pressure can range from high temperature with little or no pressure to high pressure with no increase in temperature. Thus welding can be accomplished under a wide variety of conditions, resulting in the development of numerous welding processes which are routinely used for a variety of purposes.
Given the variety and flexibility of welding techniques available, it is no surprise, then, that surfacing by welding is extensively used for the reclaimation of items damaged in service and to "hard-face" the exposed surfaces of thick walled vessels.
While all the major welding processes can be used for surfacing, the use of submerged arc welding is particularly advantageous in that the arc is maintained beneath a blanket of granular flux thus, effectively eliminating the operator's need for specialized safety clothing. The flux provides excellent shielding of the molten metal and, because the pool of molten metal is relatively large, good fluxing action occurs to remove any impurities. A portion of the flux is melted and solidifies into a glasslike covering over the weld. This, along with the flux which is not melted, provides a thermal coating that slows the cooling of the weld area and helps to produce a soft, ductile weld. The solidified flux cracks loose from the weld upon cooling (because of the differential thermal contraction) and is easily removed. Thus, submerged arc welding typically produces welds of extremely high quality using either AC or DC as the power source.
Many techniques and apparatuses for applying a weld overlay to both rectilinear and tubular surfaces utilizing submerged arc welding are to be found in the patent literature and are cited and discussed in the disclosure and specifications of Canadian Patent number 2010872 issued August 1991 to the inventor of the present invention, wherein is disclosed a device to apply longitudinally extending welds to the interior of a hollow tubular vessel, while rotating the vessel between each weld application.
One major disadvantage associated with the devices and techniques heretobefore disclosed is that such devices and techniques make no provision for applying a weld overlay to a curved hollow vessel; for example, ninety degree elbows with varying radii.
While this above mentioned shortcoming may be obviated by the modification of the device disclosed in my patent to the subject matter of the present invention nevertheless all heretobefore described devices suffer from the following shortcomings:
(a) they are restricted in use to providing a weld overlay on straight vessels; PA0 (b) they are relatively complex in construction and use; and PA0 (c) they require relatively high maintenance. PA0 (a) to provide a relatively simple device for performing submerged arc welding on the interior of a curved, hollow vessel such as a ninety degree elbow; PA0 (b) to provide an efficient method of coating the interior surface, by submerged arc welding means, of a curved hollow vessel using the device described herein; PA0 (c) to provide a method of surfacing the interior of a curved hollow article by welding such that a substantially smooth weld is produced which serves to reduce the possibility of weld defects commonly occuring by virtue of irregular weld deposits; and PA0 (d) to provide a method of coating the interior surface of curved hollow articles utilizing a submerged arc welding device of relatively simple construction and inexpensive manufacture.